\\timing --\u663e\u793aSQL\u7684\u6267\u884c\u65f6\u95f4
\n\u4e00\u3001\u4f7f\u7528EXPLAIN\uff1a<\/p>\n
PostgreSQL\u4e3a\u6bcf\u4e2a\u67e5\u8be2\u90fd\u751f\u6210\u4e00\u4e2a\u67e5\u8be2\u89c4\u5212\uff0c\u56e0\u4e3a\u9009\u62e9\u6b63\u786e\u7684\u67e5\u8be2\u8def\u5f84\u5bf9\u6027\u80fd\u7684\u5f71\u54cd\u662f\u6781\u4e3a\u5173\u952e\u7684\u3002PostgreSQL\u672c\u8eab\u5df2\u7ecf\u5305\u542b\u4e86\u4e00\u4e2a\u89c4\u5212\u5668\u7528\u4e8e\u5bfb\u627e\u6700\u4f18\u89c4\u5212\uff0c\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7\u4f7f\u7528EXPLAIN\u547d\u4ee4\u6765\u67e5\u770b\u89c4\u5212\u5668\u4e3a\u6bcf\u4e2a\u67e5\u8be2\u751f\u6210\u7684\u67e5\u8be2\u89c4\u5212\u3002\nPostgreSQL\u4e2d\u751f\u6210\u7684\u67e5\u8be2\u89c4\u5212\u662f\u75311\u5230n\u4e2a\u89c4\u5212\u8282\u70b9\u6784\u6210\u7684\u89c4\u5212\u6811\uff0c\u5176\u4e2d\u6700\u5e95\u5c42\u7684\u8282\u70b9\u4e3a\u8868\u626b\u63cf\u8282\u70b9\uff0c\u7528\u4e8e\u4ece\u6570\u636e\u8868\u4e2d\u8fd4\u56de\u68c0\u7d22\u51fa\u7684\u6570\u636e\u884c\u3002\u7136\u800c\uff0c\u4e0d\u540c\u7684\u626b\u63cf\u8282\u70b9\u7c7b\u578b\u4ee3\u8868\u7740\u4e0d\u540c\u7684\u8868\u8bbf\u95ee\u6a21\u5f0f\uff0c\u5982\uff1a\u987a\u5e8f\u626b\u63cf\u3001\u7d22\u5f15\u626b\u63cf\uff0c\u4ee5\u53ca\u4f4d\u56fe\u7d22\u5f15\u626b\u63cf\u7b49\u3002\u5982\u679c\u67e5\u8be2\u4ecd\u7136\u9700\u8981\u8fde\u63a5\u3001\u805a\u96c6\u3001\u6392\u5e8f\uff0c\u6216\u8005\u662f\u5bf9\u539f\u59cb\u884c\u7684\u5176\u5b83\u64cd\u4f5c\uff0c\u90a3\u4e48\u5c31\u4f1a\u5728\u626b\u63cf\u8282\u70b9\"\u4e4b\u4e0a\"\u6709\u5176\u5b83\u989d\u5916\u7684\u8282\u70b9\u3002\u5e76\u4e14\u8fd9\u4e9b\u64cd\u4f5c\u901a\u5e38\u90fd\u6709\u591a\u79cd\u65b9\u6cd5\uff0c\u56e0\u6b64\u5728\u8fd9\u4e9b\u4f4d\u7f6e\u4e5f\u6709\u53ef\u80fd\u51fa\u73b0\u4e0d\u540c\u7684\u8282\u70b9\u7c7b\u578b\u3002EXPLAIN\u5c06\u4e3a\u89c4\u5212\u6811\u4e2d\u7684\u6bcf\u4e2a\u8282\u70b9\u90fd\u8f93\u51fa\u4e00\u884c\u4fe1\u606f\uff0c\u663e\u793a\u57fa\u672c\u7684\u8282\u70b9\u7c7b\u578b\u548c\u89c4\u5212\u5668\u4e3a\u6267\u884c\u8fd9\u4e2a\u89c4\u5212\u8282\u70b9\u8ba1\u7b97\u51fa\u7684\u9884\u8ba1\u5f00\u9500\u503c\u3002\u7b2c\u4e00\u884c(\u6700\u4e0a\u5c42\u7684\u8282\u70b9)\u662f\u5bf9\u8be5\u89c4\u5212\u7684\u603b\u6267\u884c\u5f00\u9500\u7684\u9884\u8ba1\uff0c\u8fd9\u4e2a\u6570\u503c\u5c31\u662f\u89c4\u5212\u5668\u8bd5\u56fe\u6700\u5c0f\u5316\u7684\u6570\u503c\u3002 \n\u8fd9\u91cc\u6709\u4e00\u4e2a\u7b80\u5355\u7684\u4f8b\u5b50\uff0c\u5982\u4e0b\uff1a\nEXPLAIN SELECT * FROM tenk1;\n QUERY PLAN\n-------------------------------------------------------------\n Seq Scan on tenk1 (cost=0.00..458.00 rows=10000 width=244)\n\nEXPLAIN\u5f15\u7528\u7684\u6570\u636e\u662f\uff1a\n1). \u9884\u8ba1\u7684\u542f\u52a8\u5f00\u9500(\u5728\u8f93\u51fa\u626b\u63cf\u5f00\u59cb\u4e4b\u524d\u6d88\u8017\u7684\u65f6\u95f4\uff0c\u6bd4\u5982\u5728\u4e00\u4e2a\u6392\u5e8f\u8282\u70b9\u91cc\u505a\u6392\u7eed\u7684\u65f6\u95f4)\u3002\n2). \u9884\u8ba1\u7684\u603b\u5f00\u9500\u3002\n3). \u9884\u8ba1\u7684\u8be5\u89c4\u5212\u8282\u70b9\u8f93\u51fa\u7684\u884c\u6570\u3002\n4). \u9884\u8ba1\u7684\u8be5\u89c4\u5212\u8282\u70b9\u7684\u884c\u5e73\u5747\u5bbd\u5ea6(\u5355\u4f4d\uff1a\u5b57\u8282)\u3002 \n\u8fd9\u91cc\u5f00\u9500(cost)\u7684\u8ba1\u7b97\u5355\u4f4d\u662f\u78c1\u76d8\u9875\u9762\u7684\u5b58\u53d6\u6570\u91cf\uff0c\u59821.0\u5c06\u8868\u793a\u4e00\u6b21\u987a\u5e8f\u7684\u78c1\u76d8\u9875\u9762\u8bfb\u53d6\u3002\u5176\u4e2d\u4e0a\u5c42\u8282\u70b9\u7684\u5f00\u9500\u5c06\u5305\u62ec\u5176\u6240\u6709\u5b50\u8282\u70b9\u7684\u5f00\u9500\u3002\u8fd9\u91cc\u7684\u8f93\u51fa\u884c\u6570(rows)\u5e76\u4e0d\u662f\u89c4\u5212\u8282\u70b9\u5904\u7406\/\u626b\u63cf\u7684\u884c\u6570\uff0c\u901a\u5e38\u4f1a\u66f4\u5c11\u4e00\u4e9b\u3002\u4e00\u822c\u800c\u8a00\uff0c\u9876\u5c42\u7684\u884c\u9884\u8ba1\u6570\u91cf\u4f1a\u66f4\u63a5\u8fd1\u4e8e\u67e5\u8be2\u5b9e\u9645\u8fd4\u56de\u7684\u884c\u6570\u3002\n\u73b0\u5728\u6211\u4eec\u6267\u884c\u4e0b\u9762\u57fa\u4e8e\u7cfb\u7edf\u8868\u7684\u67e5\u8be2\uff1a\nSELECT relpages, reltuples FROM pg_class WHERE relname = 'tenk1';\n\u4ece\u67e5\u8be2\u7ed3\u679c\u4e2d\u53ef\u4ee5\u770b\u51fatenk1\u8868\u5360\u6709358\u4e2a\u78c1\u76d8\u9875\u9762\u548c10000\u6761\u8bb0\u5f55\uff0c\u7136\u800c\u4e3a\u4e86\u8ba1\u7b97cost\u7684\u503c\uff0c\u6211\u4eec\u4ecd\u7136\u9700\u8981\u77e5\u9053\u53e6\u5916\u4e00\u4e2a\u7cfb\u7edf\u53c2\u6570\u503c\u3002\npostgres=# show cpu_tuple_cost;\n cpu_tuple_cost\n----------------\n 0.01\n(1 row)\n cost = 358(\u78c1\u76d8\u9875\u9762\u6570) + 10000(\u884c\u6570) * 0.01(cpu_tuple_cost\u7cfb\u7edf\u53c2\u6570\u503c)\n\n \u4e0b\u9762\u6211\u4eec\u518d\u6765\u770b\u4e00\u4e2a\u5e26\u6709WHERE\u6761\u4ef6\u7684\u67e5\u8be2\u89c4\u5212\u3002\nEXPLAIN SELECT * FROM tenk1 WHERE unique1 < 7000;\n\n QUERY PLAN\n------------------------------------------------------------\n Seq Scan on tenk1 (cost=0.00..483.00 rows=7033 width=244)\n Filter: (unique1 < 7000)\n\nEXPLAIN\u7684\u8f93\u51fa\u663e\u793a\uff0cWHERE\u5b50\u53e5\u88ab\u5f53\u4f5c\u4e00\u4e2a\"filter\"\u5e94\u7528\uff0c\u8fd9\u8868\u793a\u8be5\u89c4\u5212\u8282\u70b9\u5c06\u626b\u63cf\u8868\u4e2d\u7684\u6bcf\u4e00\u884c\u6570\u636e\uff0c\u4e4b\u540e\u518d\u5224\u5b9a\u5b83\u4eec\u662f\u5426\u7b26\u5408\u8fc7\u6ee4\u7684\u6761\u4ef6\uff0c\u6700\u540e\u4ec5\u8f93\u51fa\u901a\u8fc7\u8fc7\u6ee4\u6761\u4ef6\u7684\u884c\u6570\u3002\u8fd9\u91cc\u7531\u4e8eWHERE\u5b50\u53e5\u7684\u5b58\u5728\uff0c\u9884\u8ba1\u7684\u8f93\u51fa\u884c\u6570\u51cf\u5c11\u4e86\u3002\u5373\u4fbf\u5982\u6b64\uff0c\u626b\u63cf\u4ecd\u5c06\u8bbf\u95ee\u6240\u670910000\u884c\u6570\u636e\uff0c\u56e0\u6b64\u5f00\u9500\u5e76\u6ca1\u6709\u771f\u6b63\u964d\u4f4e\uff0c\u5b9e\u9645\u4e0a\u5b83\u8fd8\u589e\u52a0\u4e86\u4e00\u4e9b\u56e0\u6570\u636e\u8fc7\u6ee4\u800c\u4ea7\u751f\u7684\u989d\u5916CPU\u5f00\u9500\u3002\n\u4e0a\u9762\u7684\u6570\u636e\u53ea\u662f\u4e00\u4e2a\u9884\u8ba1\u6570\u5b57\uff0c\u5373\u4f7f\u662f\u5728\u6bcf\u6b21\u6267\u884cANALYZE\u547d\u4ee4\u4e4b\u540e\u4e5f\u4f1a\u968f\u4e4b\u6539\u53d8\uff0c\u56e0\u4e3aANALYZE\u751f\u6210\u7684\u7edf\u8ba1\u6570\u636e\u662f\u901a\u8fc7\u4ece\u8be5\u8868\u4e2d\u968f\u673a\u62bd\u53d6\u7684\u6837\u672c\u8ba1\u7b97\u7684\u3002\n\u5982\u679c\u6211\u4eec\u5c06\u4e0a\u9762\u67e5\u8be2\u7684\u6761\u4ef6\u8bbe\u7f6e\u7684\u66f4\u4e3a\u4e25\u683c\u4e00\u4e9b\u7684\u8bdd\uff0c\u5c06\u4f1a\u5f97\u5230\u4e0d\u540c\u7684\u67e5\u8be2\u89c4\u5212\uff0c\u5982\uff1a\nEXPLAIN SELECT * FROM tenk1 WHERE unique1 < 100;\n\n QUERY PLAN\n------------------------------------------------------------------------------\n Bitmap Heap Scan on tenk1 (cost=2.37..232.35 rows=106 width=244)\n Recheck Cond: (unique1 < 100)\n -> Bitmap Index Scan on tenk1_unique1 (cost=0.00..2.37 rows=106 width=0)\n Index Cond: (unique1 < 100)\n\n\u8fd9\u91cc\uff0c\u89c4\u5212\u5668\u51b3\u5b9a\u4f7f\u7528\u4e24\u6b65\u89c4\u5212\uff0c\u6700\u5185\u5c42\u7684\u89c4\u5212\u8282\u70b9\u8bbf\u95ee\u4e00\u4e2a\u7d22\u5f15\uff0c\u627e\u51fa\u5339\u914d\u7d22\u5f15\u6761\u4ef6\u7684\u884c\u7684\u4f4d\u7f6e\uff0c\u7136\u540e\u4e0a\u5c42\u89c4\u5212\u8282\u70b9\u518d\u4ece\u8868\u91cc\u8bfb\u53d6\u8fd9\u4e9b\u884c\u3002\u5355\u72ec\u5730\u8bfb\u53d6\u6570\u636e\u884c\u6bd4\u987a\u5e8f\u5730\u8bfb\u53d6\u5b83\u4eec\u7684\u5f00\u9500\u8981\u9ad8\u5f88\u591a\uff0c\u4f46\u662f\u56e0\u4e3a\u5e76\u975e\u8bbf\u95ee\u8be5\u8868\u7684\u6240\u6709\u78c1\u76d8\u9875\u9762\uff0c\u56e0\u6b64\u8be5\u65b9\u6cd5\u7684\u5f00\u9500\u4ecd\u7136\u6bd4\u4e00\u6b21\u987a\u5e8f\u626b\u63cf\u7684\u5f00\u9500\u8981\u5c11\u3002\u8fd9\u91cc\u4f7f\u7528\u4e24\u5c42\u89c4\u5212\u7684\u539f\u56e0\u662f\u56e0\u4e3a\u4e0a\u5c42\u89c4\u5212\u8282\u70b9\u628a\u901a\u8fc7\u7d22\u5f15\u68c0\u7d22\u51fa\u6765\u7684\u884c\u7684\u7269\u7406\u4f4d\u7f6e\u5148\u8fdb\u884c\u6392\u5e8f\uff0c\u8fd9\u6837\u53ef\u4ee5\u6700\u5c0f\u5316\u5355\u72ec\u8bfb\u53d6\u78c1\u76d8\u9875\u9762\u7684\u5f00\u9500\u3002\u8282\u70b9\u540d\u79f0\u91cc\u9762\u63d0\u5230\u7684\"\u4f4d\u56fe(bitmap)\"\u662f\u8fdb\u884c\u6392\u5e8f\u7684\u673a\u5236\u3002\n\u73b0\u5728\u6211\u4eec\u8fd8\u53ef\u4ee5\u5c06WHERE\u7684\u6761\u4ef6\u8bbe\u7f6e\u7684\u66f4\u52a0\u4e25\u683c\uff0c\u5982\uff1a\nEXPLAIN SELECT * FROM tenk1 WHERE unique1 < 3;\n\n QUERY PLAN\n------------------------------------------------------------------------------\n Index Scan using tenk1_unique1 on tenk1 (cost=0.00..10.00 rows=2 width=244)\n Index Cond: (unique1 < 3)\n\n\u5728\u8be5SQL\u4e2d\uff0c\u8868\u7684\u6570\u636e\u884c\u662f\u4ee5\u7d22\u5f15\u7684\u987a\u5e8f\u6765\u8bfb\u53d6\u7684\uff0c\u8fd9\u6837\u5c31\u4f1a\u4ee4\u8bfb\u53d6\u5b83\u4eec\u7684\u5f00\u9500\u53d8\u5f97\u66f4\u5927\uff0c\u7136\u800c\u4e8b\u5b9e\u4e0a\u8fd9\u91cc\u5c06\u8981\u83b7\u53d6\u7684\u884c\u6570\u5374\u5c11\u5f97\u53ef\u601c\uff0c\u56e0\u6b64\u6ca1\u6709\u5fc5\u8981\u5728\u57fa\u4e8e\u884c\u7684\u7269\u7406\u4f4d\u7f6e\u8fdb\u884c\u6392\u5e8f\u4e86\u3002\n\u73b0\u5728\u6211\u4eec\u9700\u8981\u5411WHERE\u5b50\u53e5\u589e\u52a0\u53e6\u5916\u4e00\u4e2a\u6761\u4ef6\uff0c\u5982\uff1a\nEXPLAIN SELECT * FROM tenk1 WHERE unique1 < 3 AND stringu1 = 'xxx';\n\n QUERY PLAN\n------------------------------------------------------------------------------\n Index Scan using tenk1_unique1 on tenk1 (cost=0.00..10.01 rows=1 width=244)\n Index Cond: (unique1 < 3)\n Filter: (stringu1 = 'xxx'::name)\n\n\u65b0\u589e\u7684\u8fc7\u6ee4\u6761\u4ef6stringu1 = 'xxx'\u53ea\u662f\u51cf\u5c11\u4e86\u9884\u8ba1\u8f93\u51fa\u7684\u884c\u6570\uff0c\u4f46\u662f\u5e76\u6ca1\u6709\u51cf\u5c11\u5b9e\u9645\u5f00\u9500\uff0c\u56e0\u4e3a\u6211\u4eec\u4ecd\u7136\u9700\u8981\u8bbf\u95ee\u76f8\u540c\u6570\u91cf\u7684\u6570\u636e\u884c\u3002\u800c\u8be5\u6761\u4ef6\u5e76\u6ca1\u6709\u4f5c\u4e3a\u4e00\u4e2a\u7d22\u5f15\u6761\u4ef6\uff0c\u800c\u662f\u88ab\u5f53\u6210\u5bf9\u7d22\u5f15\u7ed3\u679c\u7684\u8fc7\u6ee4\u6761\u4ef6\u6765\u770b\u5f85\u3002\n\u5982\u679cWHERE\u6761\u4ef6\u91cc\u6709\u591a\u4e2a\u5b57\u6bb5\u5b58\u5728\u7d22\u5f15\uff0c\u90a3\u4e48\u89c4\u5212\u5668\u53ef\u80fd\u4f1a\u4f7f\u7528\u7d22\u5f15\u7684AND\u6216OR\u7684\u7ec4\u5408\uff0c\u5982\uff1a\nEXPLAIN SELECT * FROM tenk1 WHERE unique1 < 100 AND unique2 > 9000;\n\n QUERY PLAN\n-------------------------------------------------------------------------------------\n Bitmap Heap Scan on tenk1 (cost=11.27..49.11 rows=11 width=244)\n Recheck Cond: ((unique1 < 100) AND (unique2 > 9000))\n -> BitmapAnd (cost=11.27..11.27 rows=11 width=0)\n -> Bitmap Index Scan on tenk1_unique1 (cost=0.00..2.37 rows=106 width=0)\n Index Cond: (unique1 < 100)\n -> Bitmap Index Scan on tenk1_unique2 (cost=0.00..8.65 rows=1042 width=0)\n Index Cond: (unique2 > 9000)\n\n\u8fd9\u6837\u7684\u7ed3\u679c\u5c06\u4f1a\u5bfc\u81f4\u8bbf\u95ee\u4e24\u4e2a\u7d22\u5f15\uff0c\u4e0e\u53ea\u4f7f\u7528\u4e00\u4e2a\u7d22\u5f15\uff0c\u800c\u628a\u53e6\u5916\u4e00\u4e2a\u6761\u4ef6\u53ea\u5f53\u4f5c\u8fc7\u6ee4\u5668\u76f8\u6bd4\uff0c\u8fd9\u4e2a\u65b9\u6cd5\u672a\u5fc5\u662f\u66f4\u4f18\u3002 \n\u73b0\u5728\u8ba9\u6211\u4eec\u6765\u770b\u4e00\u4e0b\u57fa\u4e8e\u7d22\u5f15\u5b57\u6bb5\u8fdb\u884c\u8868\u8fde\u63a5\u7684\u67e5\u8be2\u89c4\u5212\uff0c\u5982\uff1a\nEXPLAIN SELECT * FROM tenk1 t1, tenk2 t2 WHERE t1.unique1 < 100 AND t1.unique2 = t2.unique2;\n\n QUERY PLAN\n--------------------------------------------------------------------------------------\n Nested Loop (cost=2.37..553.11 rows=106 width=488)\n -> Bitmap Heap Scan on tenk1 t1 (cost=2.37..232.35 rows=106 width=244)\n Recheck Cond: (unique1 < 100)\n -> Bitmap Index Scan on tenk1_unique1 (cost=0.00..2.37 rows=106 width=0)\n Index Cond: (unique1 < 100)\n -> Index Scan using tenk2_unique2 on tenk2 t2 (cost=0.00..3.01 rows=1 width=244)\n Index Cond: (\"outer\".unique2 = t2.unique2)\n\n\u4ece\u67e5\u8be2\u89c4\u5212\u4e2d\u53ef\u4ee5\u770b\u51fa(Nested Loop)\u8be5\u67e5\u8be2\u8bed\u53e5\u4f7f\u7528\u4e86\u5d4c\u5957\u5faa\u73af\u3002\u5916\u5c42\u7684\u626b\u63cf\u662f\u4e00\u4e2a\u4f4d\u56fe\u7d22\u5f15\uff0c\u56e0\u6b64\u5176\u5f00\u9500\u4e0e\u884c\u8ba1\u6570\u548c\u4e4b\u524d\u67e5\u8be2\u7684\u5f00\u9500\u662f\u76f8\u540c\u7684\uff0c\u8fd9\u662f\u56e0\u4e3a\u6761\u4ef6unique1 < 100\u53d1\u6325\u4e86\u4f5c\u7528\u3002 \u8fd9\u4e2a\u65f6\u5019t1.unique2 = t2.unique2\u6761\u4ef6\u5b50\u53e5\u8fd8\u6ca1\u6709\u4ea7\u751f\u4ec0\u4e48\u4f5c\u7528\uff0c\u56e0\u6b64\u5b83\u4e0d\u4f1a\u5f71\u54cd\u5916\u5c42\u626b\u63cf\u7684\u884c\u8ba1\u6570\u3002\u7136\u800c\u5bf9\u4e8e\u5185\u5c42\u626b\u63cf\u800c\u8a00\uff0c\u5f53\u524d\u5916\u5c42\u626b\u63cf\u7684\u6570\u636e\u884c\u5c06\u88ab\u63d2\u5165\u5230\u5185\u5c42\u7d22\u5f15\u626b\u63cf\u4e2d\uff0c\u5e76\u751f\u6210\u7c7b\u4f3c\u7684\u6761\u4ef6t2.unique2 = constant\u3002\u6240\u4ee5\uff0c\u5185\u5c42\u626b\u63cf\u5c06\u5f97\u5230\u548cEXPLAIN SELECT * FROM tenk2 WHERE unique2 = 42\u4e00\u6837\u7684\u8ba1\u5212\u548c\u5f00\u9500\u3002\u6700\u540e\uff0c\u4ee5\u5916\u5c42\u626b\u63cf\u7684\u5f00\u9500\u4e3a\u57fa\u7840\u8bbe\u7f6e\u5faa\u73af\u8282\u70b9\u7684\u5f00\u9500\uff0c\u518d\u52a0\u4e0a\u6bcf\u4e2a\u5916\u5c42\u884c\u7684\u4e00\u4e2a\u8fed\u4ee3(\u8fd9\u91cc\u662f 106 * 3.01)\uff0c\u4ee5\u53ca\u8fde\u63a5\u5904\u7406\u9700\u8981\u7684\u4e00\u70b9\u70b9CPU\u65f6\u95f4\u3002 \n\u5982\u679c\u4e0d\u60f3\u4f7f\u7528\u5d4c\u5957\u5faa\u73af\u7684\u65b9\u5f0f\u6765\u89c4\u5212\u4e0a\u9762\u7684\u67e5\u8be2\uff0c\u90a3\u4e48\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7\u6267\u884c\u4ee5\u4e0b\u7cfb\u7edf\u8bbe\u7f6e\uff0c\u4ee5\u5173\u95ed\u5d4c\u5957\u5faa\u73af\uff0c\u5982\uff1a\nSET enable_nestloop = off;\nEXPLAIN SELECT * FROM tenk1 t1, tenk2 t2 WHERE t1.unique1 < 100 AND t1.unique2 = t2.unique2;\n\n QUERY PLAN\n------------------------------------------------------------------------------------------\n Hash Join (cost=232.61..741.67 rows=106 width=488)\n Hash Cond: (\"outer\".unique2 = \"inner\".unique2)\n -> Seq Scan on tenk2 t2 (cost=0.00..458.00 rows=10000 width=244)\n -> Hash (cost=232.35..232.35 rows=106 width=244)\n -> Bitmap Heap Scan on tenk1 t1 (cost=2.37..232.35 rows=106 width=244)\n Recheck Cond: (unique1 < 100)\n -> Bitmap Index Scan on tenk1_unique1 (cost=0.00..2.37 rows=106 width=0)\n Index Cond: (unique1 < 100)\n\n\u8fd9\u4e2a\u89c4\u5212\u4ecd\u7136\u8bd5\u56fe\u7528\u540c\u6837\u7684\u7d22\u5f15\u626b\u63cf\u4ecetenk1\u91cc\u9762\u53d6\u51fa\u7b26\u5408\u8981\u6c42\u7684100\u884c\uff0c\u5e76\u628a\u5b83\u4eec\u5b58\u50a8\u5728\u5185\u5b58\u4e2d\u7684\u6563\u5217(\u54c8\u5e0c)\u8868\u91cc\uff0c\u7136\u540e\u5bf9tenk2\u505a\u4e00\u6b21\u5168\u8868\u987a\u5e8f\u626b\u63cf\uff0c\u5e76\u4e3a\u6bcf\u4e00\u6761tenk2\u4e2d\u7684\u8bb0\u5f55\u67e5\u8be2\u6563\u5217(\u54c8\u5e0c)\u8868\uff0c\u5bfb\u627e\u53ef\u80fd\u5339\u914dt1.unique2 = t2.unique2\u7684\u884c\u3002\u8bfb\u53d6tenk1\u548c\u5efa\u7acb\u6563\u5217\u8868\u662f\u6b64\u6563\u5217\u8054\u63a5\u7684\u5168\u90e8\u542f\u52a8\u5f00\u9500\uff0c\u56e0\u4e3a\u6211\u4eec\u5728\u5f00\u59cb\u8bfb\u53d6tenk2\u4e4b\u524d\u4e0d\u53ef\u80fd\u83b7\u5f97\u4efb\u4f55\u8f93\u51fa\u884c\u3002\n\n\u6b64\u5916\uff0c\u6211\u4eec\u8fd8\u53ef\u4ee5\u7528EXPLAIN ANALYZE\u547d\u4ee4\u68c0\u67e5\u89c4\u5212\u5668\u9884\u4f30\u503c\u7684\u51c6\u786e\u6027\u3002\u8fd9\u4e2a\u547d\u4ee4\u5c06\u5148\u6267\u884c\u8be5\u67e5\u8be2\uff0c\u7136\u540e\u663e\u793a\u6bcf\u4e2a\u89c4\u5212\u8282\u70b9\u5185\u5b9e\u9645\u8fd0\u884c\u65f6\u95f4\uff0c\u4ee5\u53ca\u5355\u7eafEXPLAIN\u547d\u4ee4\u663e\u793a\u7684\u9884\u8ba1\u5f00\u9500\uff0c\u5982\uff1a\nEXPLAIN ANALYZE SELECT * FROM tenk1 t1, tenk2 t2 WHERE t1.unique1 < 100 AND t1.unique2 = t2.unique2; \n QUERY PLAN\n----------------------------------------------------------------------------------------------------------------------------------\n Nested Loop (cost=2.37..553.11 rows=106 width=488) (actual time=1.392..12.700 rows=100 loops=1)\n -> Bitmap Heap Scan on tenk1 t1 (cost=2.37..232.35 rows=106 width=244) (actual time=0.878..2.367 rows=100 loops=1)\n Recheck Cond: (unique1 < 100)\n -> Bitmap Index Scan on tenk1_unique1 (cost=0.00..2.37 rows=106 width=0) (actual time=0.546..0.546 rows=100 loops=1)\n Index Cond: (unique1 < 100)\n -> Index Scan using tenk2_unique2 on tenk2 t2 (cost=0.00..3.01 rows=1 width=244) (actual time=0.067..0.078 rows=1 loops=100)\n Index Cond: (\"outer\".unique2 = t2.unique2)\n Total runtime: 14.452 ms\n\n\u6ce8\u610f\"actual time\"\u6570\u503c\u662f\u4ee5\u771f\u5b9e\u65f6\u95f4\u7684\u6beb\u79d2\u6765\u8ba1\u7b97\u7684\uff0c\u800c\"cost\"\u9884\u4f30\u503c\u662f\u4ee5\u78c1\u76d8\u9875\u9762\u8bfb\u53d6\u6570\u91cf\u6765\u8ba1\u7b97\u7684\uff0c\u6240\u4ee5\u5b83\u4eec\u5f88\u53ef\u80fd\u662f\u4e0d\u4e00\u81f4\u7684\u3002\u7136\u800c\u6211\u4eec\u9700\u8981\u5173\u6ce8\u7684\u53ea\u662f\u4e24\u7ec4\u6570\u636e\u7684\u6bd4\u503c\u662f\u5426\u4e00\u81f4\u3002\n\u5728\u4e00\u4e9b\u67e5\u8be2\u89c4\u5212\u91cc\uff0c\u4e00\u4e2a\u5b50\u89c4\u5212\u8282\u70b9\u5f88\u53ef\u80fd\u4f1a\u8fd0\u884c\u591a\u6b21\uff0c\u5982\u4e4b\u524d\u7684\u5d4c\u5957\u5faa\u73af\u89c4\u5212\uff0c\u5185\u5c42\u7684\u7d22\u5f15\u626b\u63cf\u4f1a\u4e3a\u6bcf\u4e2a\u5916\u5c42\u884c\u6267\u884c\u4e00\u6b21\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\"loops\"\u5c06\u62a5\u544a\u8be5\u8282\u70b9\u6267\u884c\u7684\u603b\u6b21\u6570\uff0c\u800c\u663e\u793a\u7684\u5b9e\u9645\u65f6\u95f4\u548c\u884c\u6570\u76ee\u5219\u662f\u6bcf\u6b21\u6267\u884c\u7684\u5e73\u5747\u503c\u3002\u8fd9\u4e48\u505a\u7684\u539f\u56e0\u662f\u4ee4\u8fd9\u4e9b\u771f\u5b9e\u6570\u503c\u4e0e\u5f00\u9500\u9884\u8ba1\u663e\u793a\u7684\u6570\u503c\u66f4\u5177\u53ef\u6bd4\u6027\u3002\u5982\u679c\u60f3\u83b7\u5f97\u8be5\u8282\u70b9\u6240\u82b1\u8d39\u7684\u65f6\u95f4\u603b\u6570\uff0c\u8ba1\u7b97\u65b9\u5f0f\u662f\u7528\u8be5\u503c\u4e58\u4ee5\"loops\"\u503c\u3002\nEXPLAIN ANALYZE\u663e\u793a\u7684\"Total runtime\"\u5305\u62ec\u6267\u884c\u5668\u542f\u52a8\u548c\u5173\u95ed\u7684\u65f6\u95f4\uff0c\u4ee5\u53ca\u7ed3\u679c\u884c\u5904\u7406\u7684\u65f6\u95f4\uff0c\u4f46\u662f\u5b83\u5e76\u4e0d\u5305\u62ec\u5206\u6790\u3001\u91cd\u5199\u6216\u8005\u89c4\u5212\u7684\u65f6\u95f4\u3002\n\u5982\u679cEXPLAIN\u547d\u4ee4\u4ec5\u80fd\u7528\u4e8e\u6d4b\u8bd5\u73af\u5883\uff0c\u800c\u4e0d\u80fd\u7528\u4e8e\u771f\u5b9e\u73af\u5883\uff0c\u90a3\u5b83\u5c31\u4ec0\u4e48\u7528\u90fd\u6ca1\u6709\u3002\u6bd4\u5982\uff0c\u5728\u4e00\u4e2a\u6570\u636e\u8f83\u5c11\u7684\u8868\u4e0a\u6267\u884cEXPLAIN\uff0c\u5b83\u4e0d\u80fd\u9002\u7528\u4e8e\u6570\u91cf\u5f88\u591a\u7684\u5927\u8868\uff0c\u56e0\u4e3a\u89c4\u5212\u5668\u7684\u5f00\u9500\u8ba1\u7b97\u4e0d\u662f\u7ebf\u6027\u7684\uff0c\u56e0\u6b64\u5b83\u5f88\u53ef\u80fd\u5bf9\u5927\u4e9b\u6216\u8005\u5c0f\u4e9b\u7684\u8868\u9009\u62e9\u4e0d\u540c\u7684\u89c4\u5212\u3002\u4e00\u4e2a\u6781\u7aef\u7684\u4f8b\u5b50\u662f\u4e00\u4e2a\u53ea\u5360\u636e\u4e00\u4e2a\u78c1\u76d8\u9875\u9762\u7684\u8868\uff0c\u5728\u8fd9\u6837\u7684\u8868\u4e0a\uff0c\u4e0d\u7ba1\u5b83\u6709\u6ca1\u6709\u7d22\u5f15\u53ef\u4ee5\u4f7f\u7528\uff0c\u4f60\u51e0\u4e4e\u90fd\u603b\u662f\u5f97\u5230\u987a\u5e8f\u626b\u63cf\u89c4\u5212\u3002\u89c4\u5212\u5668\u77e5\u9053\u4e0d\u7ba1\u5728\u4efb\u4f55\u60c5\u51b5\u4e0b\u5b83\u90fd\u8981\u8fdb\u884c\u4e00\u4e2a\u78c1\u76d8\u9875\u9762\u7684\u8bfb\u53d6\uff0c\u6240\u4ee5\u518d\u589e\u52a0\u51e0\u4e2a\u78c1\u76d8\u9875\u9762\u8bfb\u53d6\u7528\u4ee5\u67e5\u627e\u7d22\u5f15\u662f\u6beb\u65e0\u610f\u4e49\u7684\u3002<\/code><\/pre>\n\u4e8c\u3001\u6279\u91cf\u6570\u636e\u63d2\u5165\uff1a<\/p>\n
\u6709\u4ee5\u4e0b\u51e0\u79cd\u65b9\u6cd5\u7528\u4e8e\u4f18\u5316\u6570\u636e\u7684\u6279\u91cf\u63d2\u5165\u3002\n1. \u5173\u95ed\u81ea\u52a8\u63d0\u4ea4\uff1a\n\u5728\u6279\u91cf\u63d2\u5165\u6570\u636e\u65f6\uff0c\u5982\u679c\u6bcf\u6761\u6570\u636e\u90fd\u88ab\u81ea\u52a8\u63d0\u4ea4\uff0c\u5f53\u4e2d\u9014\u51fa\u73b0\u7cfb\u7edf\u6545\u969c\u65f6\uff0c\u4e0d\u4ec5\u4e0d\u80fd\u4fdd\u969c\u672c\u6b21\u6279\u91cf\u63d2\u5165\u7684\u6570\u636e\u4e00\u81f4\u6027\uff0c\u800c\u4e14\u7531\u4e8e\u6709\u591a\u6b21\u63d0\u4ea4\u64cd\u4f5c\u7684\u53d1\u751f\uff0c\u6574\u4e2a\u63d2\u5165\u6548\u7387\u4e5f\u4f1a\u53d7\u5230\u5f88\u5927\u7684\u6253\u51fb\u3002\u89e3\u51b3\u65b9\u6cd5\u662f\uff0c\u5173\u95ed\u7cfb\u7edf\u7684\u81ea\u52a8\u63d0\u4ea4\uff0c\u5e76\u4e14\u5728\u63d2\u5165\u5f00\u59cb\u4e4b\u524d\uff0c\u663e\u793a\u7684\u6267\u884cbegin transaction\u547d\u4ee4\uff0c\u5728\u5168\u90e8\u63d2\u5165\u64cd\u4f5c\u5b8c\u6210\u4e4b\u540e\u518d\u6267\u884ccommit\u547d\u4ee4\u63d0\u4ea4\u6240\u6709\u7684\u63d2\u5165\u64cd\u4f5c\u3002\n\n2. \u4f7f\u7528COPY\uff1a\n\u4f7f\u7528COPY\u5728\u4e00\u6761\u547d\u4ee4\u91cc\u88c5\u8f7d\u6240\u6709\u8bb0\u5f55\uff0c\u800c\u4e0d\u662f\u4e00\u7cfb\u5217\u7684INSERT\u547d\u4ee4\u3002COPY\u547d\u4ee4\u662f\u4e3a\u88c5\u8f7d\u6570\u91cf\u5de8\u5927\u7684\u6570\u636e\u884c\u4f18\u5316\u8fc7\u7684\uff0c\u5b83\u4e0d\u50cfINSERT\u547d\u4ee4\u90a3\u6837\u7075\u6d3b\uff0c\u4f46\u662f\u5728\u88c5\u8f7d\u5927\u91cf\u6570\u636e\u65f6\uff0c\u7cfb\u7edf\u5f00\u9500\u4e5f\u8981\u5c11\u5f88\u591a\u3002\u56e0\u4e3aCOPY\u662f\u5355\u6761\u547d\u4ee4\uff0c\u56e0\u6b64\u5728\u586b\u5145\u8868\u7684\u65f6\u5c31\u6ca1\u6709\u5fc5\u8981\u5173\u95ed\u81ea\u52a8\u63d0\u4ea4\u4e86\u3002 \n\n3. \u5220\u9664\u7d22\u5f15\uff1a\n\u5982\u679c\u4f60\u6b63\u5728\u88c5\u8f7d\u4e00\u4e2a\u65b0\u521b\u5efa\u7684\u8868\uff0c\u6700\u5feb\u7684\u65b9\u6cd5\u662f\u521b\u5efa\u8868\uff0c\u7528COPY\u6279\u91cf\u88c5\u8f7d\uff0c\u7136\u540e\u521b\u5efa\u8868\u9700\u8981\u7684\u4efb\u4f55\u7d22\u5f15\u3002\u56e0\u4e3a\u5728\u5df2\u5b58\u5728\u6570\u636e\u7684\u8868\u4e0a\u521b\u5efa\u7d22\u5f15\u6bd4\u7ef4\u62a4\u9010\u884c\u589e\u52a0\u8981\u5feb\u3002\u5f53\u7136\u5728\u7f3a\u5c11\u7d22\u5f15\u671f\u95f4\uff0c\u5176\u5b83\u6709\u5173\u8be5\u8868\u7684\u67e5\u8be2\u64cd\u4f5c\u7684\u6027\u80fd\u5c06\u4f1a\u53d7\u5230\u4e00\u5b9a\u7684\u5f71\u54cd\uff0c\u552f\u4e00\u6027\u7ea6\u675f\u4e5f\u6709\u53ef\u80fd\u906d\u5230\u7834\u574f\u3002\n\n4. \u5220\u9664\u5916\u952e\u7ea6\u675f\uff1a\n\u548c\u7d22\u5f15\u4e00\u6837\uff0c\"\u6279\u91cf\u5730\"\u68c0\u67e5\u5916\u952e\u7ea6\u675f\u6bd4\u4e00\u884c\u884c\u68c0\u67e5\u66f4\u52a0\u9ad8\u6548\u3002\u56e0\u6b64\uff0c\u6211\u4eec\u53ef\u4ee5\u5148\u5220\u9664\u5916\u952e\u7ea6\u675f\uff0c\u88c5\u8f7d\u6570\u636e\uff0c\u7136\u540e\u5728\u91cd\u5efa\u7ea6\u675f\u3002\n\n5. \u589e\u5927maintenance_work_mem\uff1a\n\u5728\u88c5\u8f7d\u5927\u91cf\u6570\u636e\u65f6\uff0c\u4e34\u65f6\u589e\u5927maintenance_work_mem\u7cfb\u7edf\u53d8\u91cf\u7684\u503c\u53ef\u4ee5\u6539\u8fdb\u6027\u80fd\u3002\u8fd9\u4e2a\u7cfb\u7edf\u53c2\u6570\u53ef\u4ee5\u63d0\u9ad8CREATE INDEX\u547d\u4ee4\u548cALTER TABLE ADD FOREIGN KEY\u547d\u4ee4\u7684\u6267\u884c\u6548\u7387\uff0c\u4f46\u662f\u5b83\u4e0d\u4f1a\u5bf9COPY\u64cd\u4f5c\u672c\u8eab\u4ea7\u751f\u591a\u5927\u7684\u5f71\u54cd\u3002\n\n6. \u589e\u5927checkpoint_segments\uff1a\n\u4e34\u65f6\u589e\u5927checkpoint_segments\u7cfb\u7edf\u53d8\u91cf\u7684\u503c\u4e5f\u53ef\u4ee5\u63d0\u9ad8\u5927\u91cf\u6570\u636e\u88c5\u8f7d\u7684\u6548\u7387\u3002\u8fd9\u662f\u56e0\u4e3a\u5728\u5411PostgreSQL\u88c5\u8f7d\u5927\u91cf\u6570\u636e\u65f6\uff0c\u5c06\u4f1a\u5bfc\u81f4\u68c0\u67e5\u70b9\u64cd\u4f5c(\u7531\u7cfb\u7edf\u53d8\u91cfcheckpoint_timeout\u58f0\u660e)\u6bd4\u5e73\u65f6\u66f4\u52a0\u9891\u7e41\u7684\u53d1\u751f\u3002\u5728\u6bcf\u6b21\u68c0\u67e5\u70b9\u53d1\u751f\u65f6\uff0c\u6240\u6709\u7684\u810f\u6570\u636e\u90fd\u5fc5\u987bflush\u5230\u78c1\u76d8\u4e0a\u3002\u901a\u8fc7\u63d0\u9ad8checkpoint_segments\u53d8\u91cf\u7684\u503c\uff0c\u53ef\u4ee5\u6709\u6548\u7684\u51cf\u5c11\u68c0\u67e5\u70b9\u7684\u6570\u76ee\u3002\n\n7. \u4e8b\u540e\u8fd0\u884cANALYZE\uff1a\n\u5728\u589e\u52a0\u6216\u8005\u66f4\u65b0\u4e86\u5927\u91cf\u6570\u636e\u4e4b\u540e\uff0c\u5e94\u8be5\u7acb\u5373\u8fd0\u884cANALYZE\u547d\u4ee4\uff0c\u8fd9\u6837\u53ef\u4ee5\u4fdd\u8bc1\u89c4\u5212\u5668\u5f97\u5230\u57fa\u4e8e\u8be5\u8868\u7684\u6700\u65b0\u6570\u636e\u7edf\u8ba1\u3002\u6362\u53e5\u8bdd\u8bf4\uff0c\u5982\u679c\u6ca1\u6709\u7edf\u8ba1\u6570\u636e\u6216\u8005\u7edf\u8ba1\u6570\u636e\u592a\u8fc7\u9648\u65e7\uff0c\u90a3\u4e48\u89c4\u5212\u5668\u5f88\u53ef\u80fd\u4f1a\u9009\u62e9\u4e00\u4e2a\u8f83\u5dee\u7684\u67e5\u8be2\u89c4\u5212\uff0c\u4ece\u800c\u5bfc\u81f4\u67e5\u8be2\u6548\u7387\u8fc7\u4e8e\u4f4e\u4e0b<\/code><\/pre>\n
\n\u4e00\u3001\u670d\u52a1\u5668\u8fdb\u7a0b\u7684\u542f\u52a8\u548c\u5173\u95ed\uff1a<\/p>\n
\u4e0b\u9762\u662fpg_ctl\u547d\u4ee4\u7684\u4f7f\u7528\u65b9\u6cd5\u548c\u5e38\u7528\u9009\u9879\uff0c\u9700\u8981\u6307\u51fa\u7684\u662f\uff0c\u8be5\u547d\u4ee4\u662fpostgres\u547d\u4ee4\u7684\u5c01\u88c5\u4f53\uff0c\u56e0\u6b64\u5728\u4f7f\u7528\u4e0a\u6bd4\u76f4\u63a5\u4f7f\u7528postgres\u66f4\u52a0\u65b9\u4fbf\u3002\npg_ctl init[db] [-D DATADIR] [-s] [-o \"OPTIONS\"]\npg_ctl start [-w] [-t SECS] [-D DATADIR] [-s] [-l FILENAME] [-o \"OPTIONS\"]\npg_ctl stop [-W] [-t SECS] [-D DATADIR] [-s] [-m SHUTDOWN-MODE]\npg_ctl restart [-w] [-t SECS] [-D DATADIR] [-s] [-m SHUTDOWN-MODE]\npg_ctl reload [-D DATADIR] [-s]\npg_ctl status [-D DATADIR]\npg_ctl promote [-D DATADIR] [-s]<\/code><\/pre>\n\u9009\u9879 \u63cf\u8ff0
\n-D \u6307\u5b9a\u6570\u636e\u5e93\u5b58\u50a8\u7684\u8def\u5f84
\n-l \u6307\u5b9a\u670d\u52a1\u5668\u8fdb\u7a0b\u7684\u65e5\u5fd7\u6587\u4ef6
\n-s \u4ec5\u6253\u5370\u9519\u8bef\u4fe1\u606f\uff0c\u4e0d\u6253\u5370\u666e\u901a\u4fe1\u606f
\n-t SECS \u5f53\u4f7f\u7528-w\u9009\u9879\u65f6\u7b49\u5f85\u7684\u79d2\u6570
\n-w \u7b49\u5f85\u76f4\u5230\u6570\u636e\u5e93\u64cd\u4f5c\u5b8c\u6210(\u5bf9\u4e8estop\u800c\u8a00\uff0c\u8be5\u9009\u9879\u65f6\u7f3a\u7701\u9009\u9879)
\n-W \u4e0d\u7b49\u5f85\u4efb\u4f55\u64cd\u4f5c\u7684\u5b8c\u6210
\n--help \u663e\u793a\u5e2e\u52a9\u4fe1\u606f
\n--version \u663e\u793a\u7248\u672c\u4fe1\u606f
\n-m \u5bf9\u4e8estop\u548crestart\u64cd\u4f5c\uff0c\u53ef\u4ee5\u6307\u5b9a\u5173\u95ed\u6a21\u5f0f
\n\u7cfb\u7edf\u5173\u95ed\u6a21\u5f0f
\nsmart \u4e0d\u5728\u63a5\u6536\u65b0\u7684\u8fde\u63a5\uff0c\u76f4\u5230\u5f53\u524d\u5df2\u6709\u7684\u8fde\u63a5\u90fd\u65ad\u5f00\u4e4b\u540e\u624d\u9000\u51fa\u7cfb\u7edf
\nfast \u4e0d\u5728\u63a5\u6536\u65b0\u7684\u8fde\u63a5\u8bf7\u6c42\uff0c\u4e3b\u52a8\u5173\u95ed\u5df2\u7ecf\u5efa\u7acb\u7684\u8fde\u63a5\uff0c\u4e4b\u540e\u9000\u51fa\u7cfb\u7edf
\nimmediate \u7acb\u5373\u9000\u51fa\uff0c\u4f46\u662f\u5728restart\u7684\u65f6\u5019\u9700\u8981\u6709\u6062\u590d\u7684\u64cd\u4f5c\u88ab\u6267\u884c<\/p>\n
\u8fd9\u91cc\u6211\u4eec\u53ea\u662f\u7ed9\u51fa\u6700\u4e3a\u5e38\u7528\u7684\u4f7f\u7528\u65b9\u5f0f\uff0c\u5373\u6570\u636e\u5e93\u670d\u52a1\u5668\u7684\u6b63\u5e38\u542f\u52a8\u548c\u5173\u95ed\u3002\n#start\u8868\u793a\u542f\u52a8postgres\u670d\u52a1\u5668\u8fdb\u7a0b\u3002\n#-D\u6307\u5b9a\u6570\u636e\u5e93\u670d\u52a1\u5668\u7684\u521d\u59cb\u76ee\u5f55\u7684\u5b58\u653e\u8def\u5f84\u3002\n#-l\u6307\u5b9a\u6570\u636e\u5e93\u670d\u52a1\u5668\u8fdb\u7a0b\u7684\u65e5\u5fd7\u6587\u4ef6\n\/> pg_ctl -w start -D \/opt\/PostgreSQL\/9.1\/data -l \/opt\/PostgreSQL\/9.1\/data\/pg_log\/startup.log\n#stop\u8868\u793a\u505c\u6b62postgres\u670d\u52a1\u5668\u8fdb\u7a0b\n#-m fast\u5728\u5173\u95ed\u7cfb\u7edf\u65f6\uff0c\u4f7f\u7528fast\u7684\u5173\u95ed\u6a21\u5f0f\u3002\n\/> pg_ctl stop -m fast -w -D \/opt\/PostgreSQL\/9.1\/data<\/code><\/pre>\n\u4e8c\u3001\u670d\u52a1\u5668\u914d\u7f6e\uff1a<\/p>\n
1. \u8bbe\u7f6e\u53c2\u6570\uff1a\n\u5728PostgreSQL\u4e2d\uff0c\u6240\u6709\u914d\u7f6e\u53c2\u6570\u540d\u90fd\u662f\u5927\u5c0f\u5199\u4e0d\u654f\u611f\u7684\u3002\u6bcf\u4e2a\u53c2\u6570\u90fd\u53ef\u4ee5\u63a5\u53d7\u56db\u79cd\u7c7b\u578b\u7684\u503c\uff0c\u5b83\u4eec\u5206\u522b\u662f\u5e03\u5c14\u3001\u6574\u6570\u3001\u6d6e\u70b9\u6570\u548c\u5b57\u7b26\u4e32\u3002\u5176\u4e2d\u5e03\u5c14\u503c\u53ef\u4ee5\u662fON\u3001OFF\u3001TRUE\u3001FALSE\u3001YES\u3001NO\u30011\u548c0\u3002\u5305\u542b\u8fd9\u4e9b\u53c2\u6570\u7684\u914d\u7f6e\u6587\u4ef6\u662fpostgresql.conf\uff0c\u8be5\u6587\u4ef6\u901a\u5e38\u5b58\u653e\u5728initdb\u521d\u59cb\u5316\u7684\u6570\u636e(data)\u76ee\u5f55\u4e0b\uff0c\u89c1\u5982\u4e0b\u914d\u7f6e\u7247\u6bb5\uff1a\n# \u8fd9\u662f\u4e00\u4e2a\u6ce8\u91ca\nlog_connections = yes\nlog_destination = 'syslog'\nsearch_path = '$user, public'\n\u4e95\u53f7(#)\u5f00\u59cb\u7684\u884c\u4e3a\u6ce8\u91ca\u884c\uff0c\u5982\u679c\u914d\u7f6e\u503c\u4e2d\u5305\u542b\u6570\u5b57\uff0c\u5219\u9700\u8981\u7528\u5355\u5f15\u53f7\u62ec\u8d77\u3002\u5982\u679c\u53c2\u6570\u503c\u672c\u8eab\u5305\u542b\u5355\u5f15\u53f7\uff0c\u6211\u4eec\u53ef\u4ee5\u5199\u4e24\u4e2a\u5355\u5f15\u53f7(\u63a8\u8350\u65b9\u6cd5)\u6216\u7528\u53cd\u659c\u625b\u5305\u56f4\u3002 \n\u8fd9\u91cc\u9700\u8981\u6ce8\u610f\u7684\u662f\uff0c\u5e76\u975e\u6240\u6709\u914d\u7f6e\u53c2\u6570\u90fd\u53ef\u4ee5\u5728\u670d\u52a1\u5668\u8fd0\u884c\u65f6\u6267\u884c\u52a8\u6001\u4fee\u6539\uff0c\u6709\u4e9b\u53c2\u6570\u5728\u4fee\u6539\u540e\uff0c\u53ea\u80fd\u7b49\u5230\u670d\u52a1\u5668\u91cd\u65b0\u542f\u52a8\u540e\u624d\u80fd\u751f\u6548\u3002\nPostgreSQL\u8fd8\u63d0\u4f9b\u4e86\u53e6\u5916\u4e00\u79cd\u4fee\u6539\u914d\u7f6e\u53c2\u6570\u7684\u65b9\u6cd5\uff0c\u5373\u5728\u547d\u4ee4\u884c\u4e0a\u76f4\u63a5\u6267\u884c\u4fee\u6539\u547d\u4ee4\uff0c\u5982\uff1a\n\/> postgres -c log_connections=yes -c log_destination='syslog'\n\u5982\u679c\u6b64\u65f6\u547d\u4ee4\u884c\u8bbe\u7f6e\u7684\u53c2\u6570\u548c\u914d\u7f6e\u6587\u4ef6\u4e2d\u7684\u53c2\u6570\u76f8\u4e92\u51b2\u7a81\uff0c\u90a3\u4e48\u547d\u4ee4\u884c\u4e2d\u7ed9\u51fa\u7684\u53c2\u6570\u5c06\u8986\u76d6\u914d\u7f6e\u6587\u4ef6\u4e2d\u5df2\u6709\u7684\u53c2\u6570\u503c\u3002\u9664\u6b64\u4e4b\u5916\uff0c\u6211\u4eec\u8fd8\u53ef\u4ee5\u901a\u8fc7ALTER DATABASE\u548cALTER USER\u7b49PostgreSQL\u7684\u6570\u636e\u5b9a\u4e49\u547d\u4ee4\u6765\u5206\u522b\u4fee\u6539\u6307\u5b9a\u6570\u636e\u5e93\u6216\u6307\u5b9a\u7528\u6237\u7684\u914d\u7f6e\u4fe1\u606f\u3002\u5176\u4e2d\u9488\u5bf9\u6570\u636e\u5e93\u7684\u8bbe\u7f6e\u5c06\u8986\u76d6\u4efb\u4f55\u4ecepostgres\u547d\u4ee4\u884c\u6216\u8005\u914d\u7f6e\u6587\u4ef6\u4ece\u7ed9\u51fa\u7684\u8bbe\u7f6e\uff0c\u7136\u540e\u53c8\u4f1a\u88ab\u9488\u5bf9\u7528\u6237\u7684\u8bbe\u7f6e\u8986\u76d6\uff0c\u6700\u540e\u53c8\u90fd\u4f1a\u88ab\u6bcf\u4f1a\u8bdd\u7684\u9009\u9879\u8986\u76d6\u3002\u4e0b\u9762\u662f\u5f53\u670d\u52a1\u5668\u914d\u7f6e\u51fa\u73b0\u51b2\u7a81\u65f6\uff0cPostgreSQL\u670d\u52a1\u5668\u5c06\u4f1a\u91c7\u7528\u54ea\u79cd\u65b9\u5f0f\u7684\u4f18\u5148\u7ea7\uff0c\u5982\uff1a\n1). \u57fa\u4e8e\u4f1a\u8bdd\u7684\u914d\u7f6e\uff1b\n2). \u57fa\u4e8e\u7528\u6237\u7684\u914d\u7f6e\uff1b\n3). \u57fa\u4e8e\u6570\u636e\u5e93\u7684\u914d\u7f6e\uff1b\n4). postgres\u547d\u4ee4\u884c\u6307\u5b9a\u7684\u914d\u7f6e\uff1b\n5). \u914d\u7f6e\u6587\u4ef6postgresql.conf\u4e2d\u7ed9\u51fa\u7684\u914d\u7f6e\u3002\n\u6700\u540e\u9700\u8981\u8bf4\u660e\u7684\u662f\uff0c\u6709\u4e9b\u8bbe\u7f6e\u53ef\u4ee5\u901a\u8fc7PostgreSQL\u7684set\u547d\u4ee4\u8fdb\u884c\u8bbe\u7f6e\uff0c\u5982\u5728psql\u4e2d\u6211\u4eec\u53ef\u4ee5\u8f93\u5165\uff1a\nSET ENABLE_SEQSCAN TO OFF;\n\u4e5f\u53ef\u4ee5\u901a\u8fc7show\u547d\u4ee4\u6765\u663e\u793a\u6307\u5b9a\u914d\u7f6e\u7684\u5f53\u524d\u503c\uff0c\u5982\uff1a\nSHOW ENABLE_SEQSCAN;\n\u4e0e\u6b64\u540c\u65f6\uff0c\u6211\u4eec\u4e5f\u53ef\u4ee5\u624b\u5de5\u67e5\u8be2pg_settings\u7cfb\u7edf\u8868\u7684\u65b9\u5f0f\u6765\u68c0\u7d22\u611f\u5174\u8da3\u7684\u7cfb\u7edf\u53c2\u6570\u3002 <\/code><\/pre>\n\u4e09\u3001\u5185\u5b58\u76f8\u5173\u7684\u53c2\u6570\u914d\u7f6e\uff1a<\/p>\n
1. shared_buffers(integer)\uff1a\n\u8bbe\u7f6e\u6570\u636e\u5e93\u670d\u52a1\u5668\u53ef\u4ee5\u4f7f\u7528\u7684\u5171\u4eab\u5185\u5b58\u6570\u91cf\u3002\u7f3a\u7701\u60c5\u51b5\u4e0b\u53ef\u4ee5\u8bbe\u7f6e\u4e3a32MB\uff0c\u4f46\u662f\u4e0d\u8981\u5c11\u4e8e128KB\u3002\u56e0\u4e3a\u8be5\u503c\u8bbe\u7f6e\u7684\u8d8a\u9ad8\u5bf9\u7cfb\u7edf\u7684\u6027\u80fd\u8d8a\u6709\u597d\u5904\u3002\u8be5\u914d\u7f6e\u53c2\u6570\u53ea\u80fd\u5728\u6570\u636e\u5e93\u542f\u52a8\u65f6\u8bbe\u7f6e\u3002\n\u6b64\u65f6\uff0c\u5982\u679c\u4f60\u6709\u4e00\u53f0\u4e13\u7528\u7684\u6570\u636e\u5e93\u670d\u52a1\u5668\uff0c\u5176\u5185\u5b58\u4e3a1G\u6216\u8005\u66f4\u591a\uff0c\u90a3\u4e48\u6211\u4eec\u63a8\u8350\u5c06\u8be5\u503c\u8bbe\u7f6e\u4e3a\u7cfb\u7edf\u5185\u5b58\u768425%\u3002\n\n2. work_mem(integer)\uff1a\nPostgreSQL\u5728\u6267\u884c\u6392\u5e8f\u64cd\u4f5c\u65f6\uff0c\u4f1a\u6839\u636ework_mem\u7684\u5927\u5c0f\u51b3\u5b9a\u662f\u5426\u5c06\u4e00\u4e2a\u5927\u7684\u7ed3\u679c\u96c6\u62c6\u5206\u4e3a\u51e0\u4e2a\u5c0f\u7684\u548cwork_mem\u5dee\u4e0d\u591a\u5927\u5c0f\u7684\u4e34\u65f6\u6587\u4ef6\u3002\u663e\u7136\u62c6\u5206\u7684\u7ed3\u679c\u662f\u964d\u4f4e\u4e86\u6392\u5e8f\u7684\u901f\u5ea6\u3002\u56e0\u6b64\u589e\u52a0work_mem\u6709\u52a9\u4e8e\u63d0\u9ad8\u6392\u5e8f\u7684\u901f\u5ea6\u3002\u7136\u800c\u9700\u8981\u6307\u51fa\u7684\u662f\uff0c\u5982\u679c\u7cfb\u7edf\u4e2d\u540c\u65f6\u5b58\u5728\u591a\u4e2a\u6392\u5e8f\u64cd\u4f5c\uff0c\u90a3\u4e48\u6bcf\u4e2a\u64cd\u4f5c\u5728\u6392\u5e8f\u65f6\u4f7f\u7528\u7684\u5185\u5b58\u6570\u91cf\u5747\u4e3awork_mem\uff0c\u56e0\u6b64\u5728\u6211\u4eec\u8bbe\u7f6e\u8be5\u503c\u65f6\u9700\u8981\u6ce8\u610f\u8fd9\u4e00\u95ee\u9898\u3002\n\n3. maintence_work_mem(integer)\uff1a\n\u6307\u5b9a\u5728\u7ef4\u62a4\u6027\u64cd\u4f5c\u4e2d\u4f7f\u7528\u7684\u6700\u5927\u5185\u5b58\u6570\uff0c\u5982VACUUM\u3001CREATE INDEX\u548cALTER TABLE ADD FOREIGN KEY\u7b49\uff0c\u8be5\u914d\u7f6e\u7684\u7f3a\u7701\u503c\u4e3a16MB\u3002\u56e0\u4e3a\u6bcf\u4e2a\u4f1a\u8bdd\u5728\u540c\u4e00\u65f6\u523b\u53ea\u80fd\u6267\u884c\u4e00\u4e2a\u8be5\u64cd\u4f5c\uff0c\u6240\u4ee5\u4f7f\u7528\u7684\u9891\u7387\u4e0d\u9ad8\uff0c\u4f46\u662f\u8fd9\u4e9b\u6307\u4ee4\u5f80\u5f80\u6d88\u8017\u8f83\u591a\u7684\u7cfb\u7edf\u8d44\u6e90\uff0c\u56e0\u6b64\u5e94\u8be5\u5c3d\u5feb\u8ba9\u8fd9\u4e9b\u6307\u4ee4\u5feb\u901f\u6267\u884c\u5b8c\u6bd5\u3002<\/code><\/pre>\n
\n\u67e5\u770b\u6570\u636e\u5e93\u6240\u5360\u78c1\u76d8\u5927\u5c0f\uff1a
\nSELECT d.datname AS Name, pg_catalog.pg_get_userbyid(d.datdba) AS Owner,
\nCASE WHEN pg_catalog.has_database_privilege(d.datname, 'CONNECT')
\nTHEN pg_catalog.pg_size_pretty(pg_catalog.pg_database_size(d.datname))
\nELSE 'No Access'
\nEND AS SIZE
\nfROM pg_catalog.pg_database d
\nORDER BY
\nCASE WHEN pg_catalog.has_database_privilege(d.datname, 'CONNECT')
\nTHEN pg_catalog.pg_database_size(d.datname)
\nELSE NULL
\nEND DESC -- nulls first
\nLIMIT 20 ;<\/h2>\n\u67e5\u770b\u8868\u6240\u70b9\u7a7a\u95f4\u5927\u5c0f\uff1a
\nSELECT
\ntable_schema || '.' || table_name AS table_full_name,
\npg_size_pretty(pg_total_relation_size('"' || table_schema || '"."' || table_name || '"')) AS size
\nFROM information_schema.tables
\nORDER BY
\npg_total_relation_size('"' || table_schema || '"."' || table_name || '"') DESC ;<\/h2>\n
\u8868\u5206\u6790\uff1a
\nVACUUM VERBOSE ANALYZE [tablename]; --\u5bf9\u5e93\u4e2d\u7684\u6240\u6709\u8868\u8fdb\u884c\u5206\u6790<\/p>\n","protected":false},"excerpt":{"rendered":"
\\timing –\u663e\u793aSQL\u7684\u6267\u884c\u65f6\u95f4 \u4e00\u3001\u4f7f\u7528EXPLAIN\uff1a PostgreSQL\u4e3a\u6bcf\u4e2a\u67e5\u8be2\u90fd\u751f\u6210\u4e00\u4e2a\u67e5\u8be2\u89c4\u5212\uff0c\u56e0\u4e3a\u9009\u62e9\u6b63\u786e\u7684\u67e5\u8be2\u8def\u5f84\u5bf9\u6027\u80fd\u7684\u5f71\u54cd\u662f\u6781\u4e3a\u5173\u952e\u7684\u3002PostgreSQL\u672c\u8eab\u5df2\u7ecf\u5305\u542b\u4e86\u4e00\u4e2a\u89c4\u5212\u5668\u7528\u4e8e\u5bfb\u627e\u6700\u4f18\u89c4\u5212\uff0c\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7\u4f7f\u7528EXPLAIN\u547d\u4ee4\u6765\u67e5\u770b\u89c4\u5212\u5668\u4e3a\u6bcf\u4e2a\u67e5\u8be2\u751f\u6210\u7684\u67e5\u8be2\u89c4\u5212\u3002 PostgreSQL\u4e2d\u751f\u6210\u7684\u67e5\u8be2\u89c4\u5212\u662f\u75311\u5230n\u4e2a\u89c4\u5212\u8282\u70b9\u6784\u6210\u7684\u89c4\u5212\u6811\uff0c\u5176\u4e2d\u6700\u5e95\u5c42\u7684\u8282\u70b9\u4e3a\u8868\u626b\u63cf\u8282\u70b9\uff0c\u7528\u4e8e\u4ece\u6570\u636e\u8868\u4e2d\u8fd4\u56de\u68c0\u7d22\u51fa\u7684\u6570\u636e\u884c\u3002\u7136\u800c\uff0c\u4e0d\u540c\u7684\u626b\u63cf\u8282\u70b9\u7c7b\u578b\u4ee3\u8868\u7740\u4e0d\u540c\u7684\u8868\u8bbf\u95ee\u6a21\u5f0f\uff0c\u5982\uff1a\u987a\u5e8f\u626b\u63cf\u3001\u7d22\u5f15\u626b\u63cf\uff0c\u4ee5\u53ca\u4f4d\u56fe\u7d22\u5f15\u626b\u63cf\u7b49\u3002\u5982\u679c\u67e5\u8be2\u4ecd\u7136\u9700\u8981\u8fde\u63a5\u3001\u805a\u96c6\u3001\u6392\u5e8f\uff0c\u6216\u8005\u662f\u5bf9\u539f\u59cb\u884c\u7684\u5176\u5b83\u64cd\u4f5c\uff0c\u90a3\u4e48\u5c31\u4f1a\u5728\u626b\u63cf\u8282\u70b9”\u4e4b\u4e0a”\u6709\u5176\u5b83\u989d\u5916\u7684\u8282\u70b9\u3002\u5e76\u4e14\u8fd9\u4e9b\u64cd\u4f5c\u901a\u5e38\u90fd\u6709\u591a\u79cd\u65b9\u6cd5\uff0c\u56e0\u6b64\u5728\u8fd9\u4e9b\u4f4d\u7f6e\u4e5f\u6709\u53ef\u80fd\u51fa\u73b0\u4e0d\u540c\u7684\u8282\u70b9\u7c7b\u578b\u3002EXPLAIN\u5c06\u4e3a\u89c4\u5212\u6811\u4e2d\u7684\u6bcf\u4e2a\u8282\u70b9\u90fd\u8f93\u51fa\u4e00\u884c\u4fe1\u606f\uff0c\u663e\u793a\u57fa\u672c\u7684\u8282\u70b9\u7c7b\u578b\u548c\u89c4\u5212\u5668\u4e3a\u6267\u884c\u8fd9\u4e2a\u89c4\u5212\u8282\u70b9\u8ba1\u7b97\u51fa\u7684\u9884\u8ba1\u5f00\u9500\u503c\u3002\u7b2c\u4e00\u884c(\u6700\u4e0a\u5c42\u7684\u8282\u70b9)\u662f\u5bf9\u8be5\u89c4\u5212\u7684\u603b\u6267\u884c\u5f00\u9500\u7684\u9884\u8ba1\uff0c\u8fd9\u4e2a\u6570\u503c\u5c31\u662f\u89c4\u5212\u5668\u8bd5\u56fe\u6700\u5c0f\u5316\u7684\u6570\u503c\u3002 \u8fd9\u91cc\u6709\u4e00\u4e2a\u7b80\u5355\u7684\u4f8b\u5b50\uff0c\u5982\u4e0b\uff1a EXPLAIN SELECT * FROM tenk1; QUERY PLAN ————————————————————- Seq Scan on tenk1 (cost=0.00..458.00 rows=10000 width=244) EXPLAIN\u5f15\u7528\u7684\u6570\u636e\u662f\uff1a 1). \u9884\u8ba1\u7684\u542f\u52a8\u5f00\u9500(\u5728\u8f93\u51fa\u626b\u63cf\u5f00\u59cb\u4e4b\u524d\u6d88\u8017\u7684\u65f6\u95f4\uff0c\u6bd4\u5982\u5728\u4e00\u4e2a\u6392\u5e8f\u8282\u70b9\u91cc\u505a\u6392\u7eed\u7684\u65f6\u95f4)\u3002 2). \u9884\u8ba1\u7684\u603b\u5f00\u9500\u3002 3). \u9884\u8ba1\u7684\u8be5\u89c4\u5212\u8282\u70b9\u8f93\u51fa\u7684\u884c\u6570\u3002 4). \u9884\u8ba1\u7684\u8be5\u89c4\u5212\u8282\u70b9\u7684\u884c\u5e73\u5747\u5bbd\u5ea6(\u5355\u4f4d\uff1a\u5b57\u8282)\u3002 \u8fd9\u91cc\u5f00\u9500(cost)\u7684\u8ba1\u7b97\u5355\u4f4d\u662f\u78c1\u76d8\u9875\u9762\u7684\u5b58\u53d6\u6570\u91cf\uff0c\u59821.0\u5c06\u8868\u793a\u4e00\u6b21\u987a\u5e8f\u7684\u78c1\u76d8\u9875\u9762\u8bfb\u53d6\u3002\u5176\u4e2d\u4e0a\u5c42\u8282\u70b9\u7684\u5f00\u9500\u5c06\u5305\u62ec\u5176\u6240\u6709\u5b50\u8282\u70b9\u7684\u5f00\u9500\u3002\u8fd9\u91cc\u7684\u8f93\u51fa\u884c\u6570(rows)\u5e76\u4e0d\u662f\u89c4\u5212\u8282\u70b9\u5904\u7406\/\u626b\u63cf\u7684\u884c\u6570\uff0c\u901a\u5e38\u4f1a\u66f4\u5c11\u4e00\u4e9b\u3002\u4e00\u822c\u800c\u8a00\uff0c\u9876\u5c42\u7684\u884c\u9884\u8ba1\u6570\u91cf\u4f1a\u66f4\u63a5\u8fd1\u4e8e\u67e5\u8be2\u5b9e\u9645\u8fd4\u56de\u7684\u884c\u6570\u3002 \u73b0\u5728\u6211\u4eec\u6267\u884c\u4e0b\u9762\u57fa\u4e8e\u7cfb\u7edf\u8868\u7684\u67e5\u8be2\uff1a SELECT relpages, reltuples FROM pg_class WHERE relname = ‘tenk1’; \u4ece\u67e5\u8be2\u7ed3\u679c\u4e2d\u53ef\u4ee5\u770b\u51fatenk1\u8868\u5360\u6709358\u4e2a\u78c1\u76d8\u9875\u9762\u548c10000\u6761\u8bb0\u5f55\uff0c\u7136\u800c\u4e3a\u4e86\u8ba1\u7b97cost\u7684\u503c\uff0c\u6211\u4eec\u4ecd\u7136\u9700\u8981\u77e5\u9053\u53e6\u5916\u4e00\u4e2a\u7cfb\u7edf\u53c2\u6570\u503c\u3002 postgres=# show cpu_tuple_cost; cpu_tuple_cost —————- 0.01 (1 row) cost = 358(\u78c1\u76d8\u9875\u9762\u6570) + 10000(\u884c\u6570) * 0.01(cpu_tuple_cost\u7cfb\u7edf\u53c2\u6570\u503c) \u4e0b\u9762\u6211\u4eec\u518d\u6765\u770b\u4e00\u4e2a\u5e26\u6709WHERE\u6761\u4ef6\u7684\u67e5\u8be2\u89c4\u5212\u3002 EXPLAIN SELECT * FROM tenk1 WHERE unique1 < 7000; QUERY PLAN ------------------------------------------------------------ Seq Scan on tenk1 (cost=0.00..483.00 rows=7033 width=244) Filter: (unique1 < 7000) EXPLAIN\u7684\u8f93\u51fa\u663e\u793a\uff0cWHERE\u5b50\u53e5\u88ab\u5f53\u4f5c\u4e00\u4e2a\"filter\"\u5e94\u7528\uff0c\u8fd9\u8868\u793a\u8be5\u89c4\u5212\u8282\u70b9\u5c06\u626b\u63cf\u8868\u4e2d\u7684\u6bcf\u4e00\u884c\u6570\u636e\uff0c\u4e4b\u540e\u518d\u5224\u5b9a\u5b83\u4eec\u662f\u5426\u7b26\u5408\u8fc7\u6ee4\u7684\u6761\u4ef6\uff0c\u6700\u540e\u4ec5\u8f93\u51fa\u901a\u8fc7\u8fc7\u6ee4\u6761\u4ef6\u7684\u884c\u6570\u3002\u8fd9\u91cc\u7531\u4e8eWHERE\u5b50\u53e5\u7684\u5b58\u5728\uff0c\u9884\u8ba1\u7684\u8f93\u51fa\u884c\u6570\u51cf\u5c11\u4e86\u3002\u5373\u4fbf\u5982\u6b64\uff0c\u626b\u63cf\u4ecd\u5c06\u8bbf\u95ee\u6240\u670910000\u884c\u6570\u636e\uff0c\u56e0\u6b64\u5f00\u9500\u5e76\u6ca1\u6709\u771f\u6b63\u964d\u4f4e\uff0c\u5b9e\u9645\u4e0a\u5b83\u8fd8\u589e\u52a0\u4e86\u4e00\u4e9b\u56e0\u6570\u636e\u8fc7\u6ee4\u800c\u4ea7\u751f\u7684\u989d\u5916CPU\u5f00\u9500\u3002 \u4e0a\u9762\u7684\u6570\u636e\u53ea\u662f\u4e00\u4e2a\u9884\u8ba1\u6570\u5b57\uff0c\u5373\u4f7f\u662f\u5728\u6bcf\u6b21\u6267\u884cANALYZE\u547d\u4ee4\u4e4b\u540e\u4e5f\u4f1a\u968f\u4e4b\u6539\u53d8\uff0c\u56e0\u4e3aANALYZE\u751f\u6210\u7684\u7edf\u8ba1\u6570\u636e\u662f\u901a\u8fc7\u4ece\u8be5\u8868\u4e2d\u968f\u673a\u62bd\u53d6\u7684\u6837\u672c\u8ba1\u7b97\u7684\u3002 \u5982\u679c\u6211\u4eec\u5c06\u4e0a\u9762\u67e5\u8be2\u7684\u6761\u4ef6\u8bbe\u7f6e\u7684\u66f4\u4e3a\u4e25\u683c\u4e00\u4e9b\u7684\u8bdd\uff0c\u5c06\u4f1a\u5f97\u5230\u4e0d\u540c\u7684\u67e5\u8be2\u89c4\u5212\uff0c\u5982\uff1a EXPLAIN SELECT * FROM tenk1 WHERE unique1 < 100; QUERY PLAN ------------------------------------------------------------------------------ Bitmap Heap Scan on tenk1 (cost=2.37..232.35 rows=106 width=244) Recheck Cond: (unique1 < 100) -> Bitmap Index Scan on tenk1_unique1 (cost=0.00..2.37 rows=106 width=0) Ind…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_eb_attr":"","footnotes":""},"categories":[89],"tags":[],"class_list":["post-1643","post","type-post","status-publish","format-standard","hentry","category-postgres-db"],"_links":{"self":[{"href":"https:\/\/oneai.eu.org\/index.php?rest_route=\/wp\/v2\/posts\/1643","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/oneai.eu.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/oneai.eu.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/oneai.eu.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/oneai.eu.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1643"}],"version-history":[{"count":1,"href":"https:\/\/oneai.eu.org\/index.php?rest_route=\/wp\/v2\/posts\/1643\/revisions"}],"predecessor-version":[{"id":1644,"href":"https:\/\/oneai.eu.org\/index.php?rest_route=\/wp\/v2\/posts\/1643\/revisions\/1644"}],"wp:attachment":[{"href":"https:\/\/oneai.eu.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1643"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/oneai.eu.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1643"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/oneai.eu.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1643"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}